Acoustical properties of the polymer liquid crystal (P41)35 in the nematic, smectic A and glass phases

Abstract

The longitudinal acoustical velocity and the absorption were measured in the polymer liquid crystal polymethylsiloxane (P41)35 from 106 °C down to - 6°C. The nematic phase is characterized by a viscoelastic behavior and a relatively large relaxation time. We do not observe any critical absorption nor at the isotropic-nematic transition neither at the nematic-smectic A transition. In the smectic A phase, we observe a regular increase of the velocity anisotropy and of the elastic coefficients C11, C13 and C 33. The transition toward the glass phase is marked by a strong maximum in the absorption around 40 °C. The four elastic constants C 11, C13, C33 and C44 were measured : C11, C33 and C44 increase if the temperature decreases but C 13 decreases